六羟甲基三聚氰胺的甲醚化反应机理分析及动力学研究

Mechanism and Kinetics of Hexamethylolmelamine Methyl Etherification

在硝酸催化下进行六羟甲基三聚氰胺(HMM)与甲醇的甲醚化反应,生成了六甲氧基甲基三聚氰胺(HMMM)。考察了反应过程中甲醇浓度的变化,提出了HMM甲醚化反应的机理并建立了动力学模型。通过实验数据拟合出醚化动力学参数,分析了不同反应温度下醚化度-时间关系。结果表明,该反应是典型的可逆平衡反应,pH=3.5下,当温度由30℃升高至55℃时,甲醚化反应平衡常数由1.17增大至2.79。甲醚化正逆反应速率常数与温度的关系分别为k1=8.54×10~6×exp(-5.39×10~4/RT)与k2=257×exp(-2.79×10~4/RT)。根据van't Hoff方程计算了该甲醚化反应表观反应焓为25.97 k J×mol^(-1),表观反应熵为86.5 J×(mol·K)^(-1)。

Hexamethoxymethyl melamine （HMMM） was synthesized through etherification of hexamethylolmelamine （HMM） with methanol using nitric acid as a catalyst. Changes of methanol concentration were determined to study the etherification process, and a kinetic model was established based on the proposed etherification mechanism. The kinetic parameters were obtained via experimental data fitting. The relationship between degree of etherification （DOE） and reaction time under different temperatures was analyzed. The results show that the etherification process is a typical reversible equilibrium reaction. The equilibrium constant of etherification increases from 1.17 to 2.79 when the temperature increases from 30℃ to 55℃ at pH 3.5. The variation of forward and reverse reaction rate constants on reaction temperature were obtained as follows： k1=8.54×10^6×exp（-5.39×10^4/RT）, k2=257×exp（-2.79×10^4/RT）. According to van ＇t Hoff equation, the apparent reaction enthalpy and reaction entropy for etherification are 25.97 kJ·mol^-1 and 86.5 J.（mol·K）^-1, respectively.